Why no long telephoto for E-mount?

In "camera time," E-mount has been around for quite a while now yet no one has made a long telephoto for it. By long I mean 500 mm or so. It seems to me the one big gap in the lens lineup, the longest being 210 mm.

Is it technical? Perhaps something to do with Sony's in-lens IS?

Or -- perhaps more likely -- is it marketing in that the manufacturers have decided that folks who buy these relatively small cameras are not going to be interested in hanging a large, four pound telephoto on it?